Process of preparing pure zinc-sulfate solution from zinc ores.



UTEI) STATES PATENT OFFICE- SHUNJ'IRO ARAKI, OF OSAKA, JAPAN.

PROCESS OF PREPARING PURE ZINC-SULFATE SOLUTION FROM. Z-INC-ORES.

No Drawing.

To all whom it may concern:

Be it known that I, SHUNJIRO ARAKI, a

subject of the Emperor of Japan, and a resident of the city of Osaka, Japan, have invented certain new and useful Improvements in Processes of Preparing Pure Zinc- Sulfate Solution from Zinc Ores, of which the following is a specification.

This invention relates to a process of preparing a pure zinc sulfate'solution; and it comprises a process of preparing such a solution from zinc ores, and particularly from roasted zinc ores of a silicate nature, by treating the roasted ore with the chemical equivalent of a sodium bisulfate solution to dissolve out the zinc as well as other metals soluble in this reagent, then removing from the resulting solution the heavier metals by treatment with zinc in the form of sheets or dust, subsequently neutralizing the filtrate with alkali and mixing therewith a. suitable oxidizing agent to precipitate the greater portion of the impurities such as iron, manganese,etc., and finally boiling the partially purified solution withhydrated silica or SlllClO acid, formed by neutralizing the sodium silicate with acids, to remove the remainder of the iron and manganese; audit also comprises, as a novel subprocess,

the removal of small amounts of iron and manganese from such partially purified solutions by the precipitation therein of gelatinous and colloidal silicic acid, by the decomposition of sodium silicate with a suitable acid, the gelatinous nature of this precipitate causing a separation of-most of the iron and manganese present, and the solution being subsequently heated to convert the soluble colloidal silica into the form of an insoluble gelatinous precipitate, by means of which the remaining traces of dissolved iron and manganeseare removed; all as more fully hereinafter set forth and as claimed.

In the extraction of zinc from its ores it is difiicult to obtain solutions of zinc free from objectionable impurities. In ores, particularly roasted ores of a silicate nature, there is present after roasting a considerable amount of other metals such as copper, lead, silver, iron, manganese, etc., which can be readily removed in part, but whose complete removal is attended with unusual difiiculty.

Iron and manganese are readily oxidized to form the gelatinous iron hydroxid and manganese dioxid but these compounds tendto Specification of Letters Patent.

Patented-June 6, 1916.

Application filed September 6, 1913. Serial No. 788,367."

remain in solution so that the removal of the last traces is difficult to efi'ect." Moreover, manganese dioxid, particularly in hot solutions, is present in exceedingly fine particles which pass through ordinary filtering mediums. According to the present invention these disadvantages are overcome and all objectionable impurities, such as already indicated, are removed from the zinc solution, including the dissolved iron hydroxid, probably present in the form of a colloidal S01, and the finely divided manganese dioxid. As a result a pure ZlI1C solution is' obtained from which pure white zinc oxid can be readily produced or from which pure metallic zinc can be separated by electrolysis.

According to the present invention the pulverized roasted ore is treated withthe chemical equivalent of a 20% sodium bisulfate solution, the solution or leaching being promoted by stirring. sodium bisulfate used is suflicient to extract all of the zinc, together with greater or less amounts of other metals soluble in this reagent. In such roasted ores lead is usually also present in the form of a silicate, which is decomposed by the sodium bisulfate solution. The action of this reagent, however, is much feebler than sulfuric acid upon iron and manganese compounds so that relatively less amounts ofthese metals are present in the'resulting solution. The copper present in the ore is usually decomposed and dissolved along with the zinc. For effecting dissolution of the desired metals the mixture is heated to about 100"C. for about 30 minutes, then boiled with warm water and filtered through a suitable filtering apparatus. The resulting solutionor filtrate contains the copper and zinc in solution together with lead and small amounts of silver, iron, manganese, etc. From this solution the heavy metals such as copper and lead are removed by means of zinc/fused in such form as sheets or zinc dust, this reagent serving to separate out and remove these metals from the solution. The solution is next neutralized with an alkali, such as caustic soda and a suitable oxidizing agent added to effect oxidation of the-iron and manganese. Variousoxidizing agents The amount of thecan be used such'as air and bleaching pow-fa Most of the form. of manganese dioxid or hYdI'OXida There remain, however, small amounts of both of these metals in a form-probably in a colloidal form such that their removal is exceedingly diilicult. More or less ofthe iron remains dissolved, probably as a colloidal form, and the manganese also is diflicult to remove completely from the solution because of its finely divided or dissolved nature. According to the present invention the remaining small amounts of these metals are removed by boiling the solution with ble form and is also precipitated inform of gelatinous silica, carrying down with it and removing from the zinc solution the last traces of dissolved iron andmanganese.

While I do not desire to be limited by any theoretical explanation of the exact nature of the action of the silicic acid, yet the action of the. silicic acid appears to be both that of a precipitant as well as that of a coagulant, throwing outof solution'any iron and manganese present in a state of colloidal solution, and coagulating and carrying down with it also any finely suspended insoluble compounds of these metals. As a ,result'the solution is entirely free from the last traces of these impurities so that it can be used directly without further purification as a pure zinc solution. By the'present process it iS possible to remove the indicated impurities readily by filtration since they are carried along with, and separated at'the same time as, the precipitated and insoluble silicic acid or silica. The silicic acid moreover acts as a clarifying agent and removes from the solution all traces of suspended impurities in addition to the last traces of iron and manganese. From the pure zinc sulfatesolution, white zinc oxid can be obtained which is free from impurities and which does not darken in color upon standing. Pure compact metallic zinc can be also obtained from this solution by electrolysis,'a result heretofore diflicult to attain practically.

By the use of sodium bisulfate in extracting the ore the difficultlyii'emovable im urities such as iron and manganese are re need to a minimum at the outset so that subsequent purification steps are much simplified. By the subsequent step of removing the last traces of these impurities by silicic acid the solution, which has been maintained in a relatively pure condition throughout the process,is finally freed from the remaining traces of impurities and the desired pure zinc sulfate solution obtained. The present process accordingly is one in which only small amounts of impurities are dealt with throughout the process and one from which substantially .all impurities are removed.

The processmoreover can be carried out in therefrom the last traces of finely divided suspended particles, or the last traces of dissolved colloidal, metal compounds, and accordingly I claim the invention thus generically, in addition to claiming it specifically in the purification of zinc sulfate solutions, with which, as already pointed out, it presents peculiar advantages. I

I claim 1; The process of producing a pure zinc sulfate solution from zinc ores which comprises extracting the ores with a sodium bisulfate solution, removing from the solution the heavier metals by treatment with metallic zinc, separating the greater part of the iron and manganese by neutralizing with alkali and by treatment with an oxidizing .agent, and removing the remainder of the iron and manganese by adding sodium silicate, neutralizing the sodium silicate with sulfuric acid to form silicic acid andsodium sulfate, and heating the resultingsolution containing silicic acid to convert the dissolved colloidal silicic acid into an insoluble form.

2. The process of producing a-pure zinc sulfate solution from zinc ores which comprises extracting the ores with an alkali bisulfate solution, removing from the solution the heavier metals by treatment with metallic zinc, separating the greater part of the iron andmanganese by neutralizing with alkali and by treatment with an oxidizing agent, and removing the remainder of the iron and manganese by adding an alkali silicate, neutralizing the alkali silicate with sulfuric acid to form'silicic acid and an alkali sulfate, and heating the resulting solution containing silicic acid to convert the dissolved colloidal silicic acid into an insolubl e form. v

3. The process of removing from 'zinc solutions the last traces of iron and manganese which comprises boiling such solutions with hydrated silicic acid to convert the silicic acid into an insoluble, form.

4. The process of removing from zinc sulfate solutions the last traces of iron and manganese which comprises adding a soluble alkali silicate, neutralizing the alkali silicate with sulfuric acid to form silicic acid and an alkali sulfate, and boiling the solu- 5 tion containing silicic acid to convert the dissolved silicic acid into an insoluble form.

5. The process of removing from zinc solutions the last traces of iron'and manganese which comprises neutralizing sodium sili- 10 cate in such solution with an acid to set free silicic acid, and boiling the resulting solution to convert the dissolved colloidal silicic acid into an insoluble form.

In testimony whereof I have signed this specification in the presence of two subscrib- 15 ing witnesses.

SHUNJIRO ARAKI. Witnesses:

M. KIKUoHI, V. EBIHARAI-I. 

